Preheat the oven to 180°C / 350°F. Then, cut the butternut squash into 1 inch thick cubes. The easiest way to do this is to first slice the stem off, then slice lengthways, and scoop out the seeds with a spoon. Next, place the squash halve cut-side face-down and slice horizontally across (~1 inch thick pieces). Now, it's much easier to cut the skin off with your knife, and then into cubes. Add to a lined baking tray.
Then, pierce the tomatoes with a knife so they don't explode in the oven and add to the same tray. Quarter the onion and add to the tray. Squeeze one lemon over everything followed by the olive oil. Mix well and distribute evenly on the baking tray. Place it in the oven and cook for 40 minutes, stirring half way through.
About 20 minutes before the oven timer goes off, start boiling the water for the pasta and cook according to its instructions. Don't forget to save the pasta water for later!
When the squash, tomatoes, and onion are slightly browned, add them to a blender or food processor. (Note: do not add to a sealed blender like a Nutribullet or the heat will cause pressure to build-up and explode.) Blend everything along with the other squeezed lemon, the stock cube, and reserved pasta water - add a quarter cup of pasta water at a time until desired consistency.
Pour the sauce over the cooked noodles and mix well. Top with your choice of protein. Enjoy!